Transmission, infectivity, and antibody neutralization of an emerging SARS-CoV-2 variant in California carrying a L452R spike protein mutation (preprint)

We identified a novel SARS-CoV-2 variant by viral whole-genome sequencing of 2,172 remnant nasal/nasopharyngeal swab samples from 44 counties in California. Named B.1.427/B.1.429 or 20C/L452R, the variant emerged around May 2020 and increased from 0% to >50% of sequenced cases from September 1, 2020 to January 29, 2021, exhibiting an estimated 18.6-24% increase in transmissibility relative to wild-type circulating strains. This variant is characterized by three mutations in the spike protein, including a L452R substitution in the receptor-binding domain. Our analyses revealed 2-fold increased B.1.427/B.1.429 viral shedding in vivo and increased L452R pseudovirus infection of cell cultures and lung organoids, albeit decreased relative to pseudoviruses carrying the N501Y mutation found in SARS-CoV-2 variants of concern (B.1.1.7, B.1.351, and P.1 lineages). Antibody neutralization assays showed 4.0 to 6.7-fold and 2.0-fold decreases in neutralizing titers from convalescent patients and vaccine recipients, respectively. The increased prevalence of a more transmissible variant in California associated with decreased antibody neutralization warrants further investigation.

Hospital-Based Donor Recruitment and Pre-Donation Serologic Testing for COVID-19 Convalescent Plasma (preprint)

BackgroundMajor blood centers perform serologic testing on potential COVID-19 convalescent plasma donors retrospectively after blood donation. A hospital-based recruitment program for COVID-19 convalescent plasma (CCP) donors may be an efficient way to prospectively identify potential donors. Study Design and MethodsPatients who recovered from known or suspected COVID-19 were identified and recruited through medical record searches and public appeals. Participants were screened with a modified donor history questionnaire (DHQ), and if eligible, were consented and tested for SARS-CoV-2 antibodies (IgG and IgM). Participants who were positive for SARS-CoV-2 IgG were referred to a local blood center for convalescent plasma collection. ResultsOf 179 individuals screened, 128 completed serologic testing and 89 were referred for convalescent plasma donation to a local blood center (49.7% of those screened). IgG antibodies to SARS-CoV-2 were detected in 23/51 (45.1%) of participants with suspected COVID-19 and in 66/77 (85.7%) of participants with self-reported PCR-confirmed COVID-19. Testing was performed at a median of 38 days since last symptoms. Participant age positively correlated with anti-SARS-CoV-2 IgG and IgM levels. Time since last symptoms did not correlate with IgG or IgM levels. A wide range of SARS-CoV-2 IgG levels were observed. ConclusionA hospital based CCP donor recruitment program can prospectively identify potential CCP donors. Variability in SARS-CoV-2 IgG levels has implications for selection of CCP units for transfusion.

SARS-CoV-2 seroprevalence and neutralizing activity in donor and patient blood from the San Francisco Bay Area (preprint)

We report very low SARS-CoV-2 seroprevalence in two San Francisco Bay Area populations. Seropositivity was 0.26% in 387 hospitalized patients admitted for non-respiratory indications and 0.1% in 1,000 blood donors. We additionally describe the longitudinal dynamics of immunoglobulin-G, immunoglobulin-M, and in vitro neutralizing antibody titers in COVID-19 patients. Neutralizing antibodies rise in tandem with immunoglobulin levels following symptom onset, exhibiting median time to seroconversion within one day of each other, and there is >93% positive percent agreement between detection of immunoglobulin-G and neutralizing titers.

Test performance evaluation of SARS-CoV-2 serological assays (preprint)

Background Serological tests are crucial tools for assessments of SARS-CoV-2 exposure, infection and potential immunity. Their appropriate use and interpretation require accurate assay performance data. Method We conducted an evaluation of 10 lateral flow assays (LFAs) and two ELISAs to detect anti-SARS-CoV-2 antibodies. The specimen set comprised 128 plasma or serum samples from 79 symptomatic SARS-CoV-2 RT-PCR-positive individuals; 108 pre-COVID-19 negative controls; and 52 recent samples from individuals who underwent respiratory viral testing but were not diagnosed with Coronavirus Disease 2019 (COVID-19). Samples were blinded and LFA results were interpreted by two independent readers, using a standardized intensity scoring system. Results Among specimens from SARS-CoV-2 RT-PCR-positive individuals, the percent seropositive increased with time interval, peaking at 81.8-100.0% in samples taken >20 days after symptom onset. Test specificity ranged from 84.3-100.0% in pre-COVID-19 specimens. Specificity was higher when weak LFA bands were considered negative, but this decreased sensitivity. IgM detection was more variable than IgG, and detection was highest when IgM and IgG results were combined. Agreement between ELISAs and LFAs ranged from 75.7-94.8%. No consistent cross-reactivity was observed. Conclusion Our evaluation showed heterogeneous assay performance. Reader training is key to reliable LFA performance, and can be tailored for survey goals. Informed use of serology will require evaluations covering the full spectrum of SARS-CoV-2 infections, from asymptomatic and mild infection to severe disease, and later convalescence. Well-designed studies to elucidate the mechanisms and serological correlates of protective immunity will be crucial to guide rational clinical and public health policies.